If greenhouse gas emissions continue to increase, global warming could signify the virtual extinction of polar bears by the end of the century. This is the conclusion of a study published Monday in Nature Climate Change . Researchers have looked at the biggest threat facing polar bears today: the gradual disappearance of their habitat, the ice floe, from where they catch seals essential for their food. The carnivore, which lives in arctic regions where the temperature can drop to -40 ° C in winter, can fast for months, especially during the summer period when the ice floe melts every year.
Melting pack ice prevents food
But with global warming, twice as fast in the Arctic, the absence of ice lasts longer and longer. Unable to find another food as rich as seals in their environment, more and more hungry bears sometimes venture far from their territory, near inhabited areas. The melting of the ice floe is a challenge in particular for the females, who enter their den in the fall to give birth in the middle of the winter and emerge in the spring with their cubs.
"They must then catch enough seals to store enough fat and produce enough milk to feed their young throughout the summer fast," said Steven Amstrup, one of the study's authors, and told AFP. chief scientist of the NGO Polar Bears International. "By estimating the maximum and minimum weight of bears, and by modeling their energy expenditure, we calculated the limit number of fasting days that a polar bear can support before the survival rate of adults and young begins to decline", adds Peter Molnar of the University of Toronto.
For example, a male from the Hudson Bay subpopulation 20% below normal at the start of the fast would only survive 125 days, compared to 200 today.
Fall in reproduction
The approximately 25,000 polar bears are distributed into 19 distinct subpopulations in Canada, Alaska, Siberia, Svalbard and Greenland, some of which are poorly understood. According to the study published Monday, these groups will not all be affected at the same rate. But if greenhouse gas emissions continue at the same rate as today, "the fall in reproduction and survival will endanger the persistence of almost all sub-populations by 2100" , conclude the researchers. With the possible exception of Queen Elizabeth Island, notes Steven Amstrup.
And even if the warming was limited to 2.4 ° C compared to the pre-industrial era (almost half a degree above the objective of the Paris Agreement), that "would not guarantee save polar bears in the long term, "insists the scientist. "If by magic, even with the increase in temperatures, the ice pack continues, it would probably be good for polar bears. But their habitat literally melts with the rise in temperatures."
Kill the last bears?
The planet has gained more than 1 ° C since the pre-industrial era, already leading to an increase in heat waves, droughts or floods. And while the current commitments of states will lead to a world at + 3 ° C, these extreme weather events are bound to worsen with each additional half degree. Classifying the polar bear as "critically endangered" on the famous red list of the International Conservation Union (IUCN), which considers them only "vulnerable", would probably not change the fate of the arctic plantigrade.
Many endangered species are endangered by poaching or the direct destruction of their habitat by humans. But "you can't build a fence to protect polar bears from the rising temperature," said the scientist at Polar Bears International. To save the species, some evoke a reintroduction of animals bred in captivity, even their move towards Antarctica. Unfeasible, according to Steven Amstrup. "It may be necessary to consider killing the last polar bears, instead of letting them starve."